Digital phase control for ink jet printer

ABSTRACT

Phase control device for an ink jet printer in which the phase between ink droplet forming means and the droplet charging means is adjusted and maintained by using the reset signal of a ring counter of predetermined capacity and changing the number of pulses in a train producing cycling of the counter. The counter is normally supplied with clock pulses at a frequency which is an integral multiple of the frequency of droplet formation and counter capacity is such that reset signals nominally occur at the same frequency as the droplet formation so that charging signals can be applied in phase with the formation of droplets. For unwanted droplets, a sawtooth wave is applied to the charge plate so that the charge on the droplet depends on the exact moment of drop break-off. The magnitude of the sawtooth wave is such that all unwanted droplets strike a gutter. The location of droplet impact on the gutter is sensed and the pulse train to the counter is changed by either adding or deleting a pulse to thereby change the time of the reset and initiation signals by a fraction of the droplet formation frequency.

United States Patent Meier Feb. 11, 1975 DIGITAL PHASE CONTROL FOR INKJET [57] ABSTRACT PRINTER Phase control device for an ink jet printer inwhich the [75] Inventor, Johann Hans Meier Vestal, phase between inkdroplet forming means and the droplet charging means is adjusted andmaintained by Asslgneei lmematlfnal Business Machines using the resetsignal of a ring counter of predeter- Corporatlon, Armonk mined capacityand changing the number of pulses in [22] Filed: June 22 1973 a trainproducing cycling of the counter. The counter is normally supplied withclock pulses at a frequency PP 372,897 which is an integral multiple ofthe frequency of drop let formation and counter capacity is such thatreset 52 us. Cl. 346/75 Signals mmihalh the Same frequency as 511 Int.Cl. G01d 18/00 droplet formahm' 50 that charging signals can he [58]Field of Search 346/75 P in Phase with the fOrmaho" of dmplets' Forwanted droplets, a sawtooth wave is applied to the [56] References Citedcharge plate so that the charge on the droplet depends on the exactmoment of drop break-off. The magni- UNTED STATES PATENTS tude of thesawtooth wave is such that all unwanted 3,596,276 7/l97l Lovelady 346/75X droplets strike a gutter The location f droplet impact gm on thegutter is sensed and the pulse train to the 3769632 /1973 E ";{;i 346/75counter is changed by either adding or deleting a pulse to therebychange the time of the reset and initiation Primary Ewminer joseph wHartary signals by a fraction of the droplet formation fre- Altorney,Agent, or Firm-Kenneth P. Johnson quency 12 Claims, Drawing Figures cmBINARY FREQUENCY 46 warm \/\/\1 DIVIDER CHARACTER DRIVE 27 SELECTIONCHARACTER f1 GENERATOR cHARGlNG CIRCUIT rumour "nil-L 66 DRlVER 15 30DISCARD mv omcmc CIRCUIT 32 B5 r64 167 AND 68 L, i S LATCH L s so 62SHARPENER 70 n 6 I s; OR 3 "als F AND COUNTER 53 F 52 53 '38 my NAND ANDAND 54 37 PATENTED FEB] 1 1975 SHEET 2 BF 2 1)CLOCKPULSESM u)CLOCKPULSESm b) SAMPLE SIGNAL V b) SAMPLE SIGNAL J\ c)LATCH65 L c)LATCH 63d)INVERTER65 m d)INVERTER65 e)AND64 l e)AND64 f)LATCH6Y J l f)LATCH67 Lg)AND68 l g)AND68 1 FIG. 2 FIG. 3

u) CLOCKQPULSES W b) SAMPLE SIGNAL L c) COMPARATOR 51 e) SINGLE SHOT 10d) AND 68 r) SINGLE SHOT n 9) AND 36 FIG. 4

u) CLOCK PULSES W b)S|GNAL SIGNAL M FIG. 5

DIGITAL PHASE CONTROL FOR INK JET PRINTER CROSS-REFERENCE TO RELATEDAPPLICATIONS A portion of the apparatus herein disclosed is part of thesubject matter of a patent application entitled Phase Control for InkJet Printer, Ser. No. 253,065, filed May I5, 1972 by J. W. Haskell, nowabandoned and refiled as a continuation, Ser. No. 380,641 on July 7,1973 and assigned to the assignee of the instant application.

FIELD OF THE INVENTION This invention relates generally to ink jetprinters and more particularly to apparatus for maintaining the properphase relationship between the droplet forming means and chargingvoltage for each droplet.

DESCRIPTION OF THE PRIOR ART The phase relationship between the appliedcharging voltage and the droplet formation is critical to the accurateplacement of the droplets upon a printing surface. When the droplet isformed during the transition from one charging voltage to another,deflection cannot be predicted and drops are misplaced on the printingsurface, generally resulting in deformed characters. In the past,attempts to insure the proper phase relationship have employed usuallyan analog circuit to change the relationship or have employed coarseadjustments such as 180 or 90 of phase shift which then becomes anapproximation if the phase should have been corrected by differentamounts.

During operation of the prior art phase control circuits, there is atendency for voltage levels to gradually shift so that accurate phasemaintenance deteriorates. Also in the prior art, the correction signalwhich is determined to be necessary is used to control a delay circuitwhich is satisfactory for the coarse adjustments but makes fineadjustments in the phase relationship nearly impossible unless elaboratedelay networks are employed.

Some of the correction circuits used in the past also set aside specialphase checking times during operation. However, the above mentionedapplication, Ser. No. 253,065, discloses a scheme wherein each unusedink droplet is given a calibration charge and the impact region of thatdiscarded droplet can be detected and appropriate corrections made. Thispermits the phase correction to occur at random times without waitinguntil special testing cycles can be made.

It is accordingly a primary object of this invention to provide a newand novel phase control system for an ink jet printer which employsdigital signals to attain the necessary phase shift.

Another important object of this invention is to provide apparatus forphase shift control for an ink jet printer in which the increments ofadjustment can be of nearly any desired size.

A further object of this invention is to provide a phase control systemfor an ink jet printer in which a ring counter of predetermined capacityis continuously supplied with clock pulses and the charge application toink droplets depends upon the time of reset of the ring counter.

A still further object of this invention is to provide a phase controlsystem for an ink jet printer in which phase correction can occur over awide range of time intervals.

It is also an important object of this invention to provide a phasecontrol system for an ink jet printer in which phase change isbi-directional and in which the system will automatically find a regionof optimum performance and then hunt by discrete steps about the optimumpoint.

SUMMARY OF THE INVENTION The foregoing objects are attained inaccordance with the invention by providing a clock pulse generator thathas a frequency that is an integral multiple of the frequency of the inkdroplet forming means. The droplet forming means is operated through afrequency divider and the clock output is directly connected to a ringcounter through gating logic circuits. The capacity of the ring counteris equal to the integral multiple of clock pulses per droplet generated.The output of the ring counter during reset provides an initiationsignal for both the character generator circuit and the sawtoothcalibration charging circuit for discarded droplets, which in turncontrols the voltage application to the charging plates at the time ofdroplet formation.

Discard droplets charged by the ramp voltages will fall into one of apair of impact locations in a gutter according to the ramp voltage levelat the time of droplet formation. Droplet impact is detected and asignal is generated as to which impact area the discard droplets areimpinging upon. These impact signals are used to control the abovementioned logic circuits to either suppress one count or add one countto the pulse train which is supplied by the clock to the ring counter.Thus, the time at which the reset signal occurs in the ring countervaries at each correction, either approximately one clock pulse periodearlier or one clock pulse period later.

The timing of the pulse train alterations is controlled through asampling pulse which can be supplied at regular or randomly selectedintervals. The sampling pulse activates gating circuits which willpermit the addition or deletion of a clock pulse to the ring counter.The gating circuits also assure that pulse deletion or addition willoccur at the proper time to avoid interference with the regularlygenerated clock pulses.

This invention has the advantage of permitting smaller increments ofadjustment than heretofore possible. For example, in the embodiment tobe described, the clock pulse frequency is 1 MHz while the dropletformation is at KHz. Thus, incremental adjustments are 45 for eachchange. Only one alteration of the normal clock train is permitted inany one counting cycle. By using discard drops as a means for testingthe phase relationship, correction can be made at various intervals. Forexample, the sampling pulse, if desired, can be produced about asfrequently as each millisecond or at greater time intervals such as 15to 20 milliseconds, depending upon the amount of control necessary forproper drop deflection. In the embodiment disclosed, the discard dropsdo not impact a correct position in the gutter. Instead when impactoccurs in one of two gutter positions, the correction circuits changethe direction of phase shift to move the discard drop impact into theother gutter location.

This phase control circuit uses only digital signal levels, and henceavoids the need for close discrimination as required by analog circuits.The control circuit is simplified in arrangement and does not requirecomplex special circuits.

The foregoing and other objects, features and advantages of theinvention will be apparent from the following more detailed descriptionof preferred embodiments of the invention as illustrated in theaccompanying drawing.

DESCRIPTION OF THE DRAWING In the drawing.

FIG. I is a schematic circuit diagram of a phase control system for anink jet printer constructed in accordance with the invention;

FIGS. 2-5 are timing diagrams of signals illustrating variousembodiments during operation of the phase control system of FIG. 1.

DESCRIPTION OF PREFERRED EMBODIMENTS Referring to FIG. 1, referencenumeral denotes ink droplet generating and deflecting apparatus usuallyemployed in an ink jet printer system. Ink from supply 11 is broughtthrough duct 12 and pressurized by pump 13 to issue from nozzle 14 whichis vibrated by transducer 15 to form individual droplets in the vicinityof a pair of charging electrodes 16. The voltage applied across thenozzle and electrodes 16 is varied to induce differing charges on thedroplets as formed, which then pass between deflecting electrodes 18connected to a high voltage source providing a constant electric field.The droplets are thereby caused to move in a trajectory determined bythe individual charge each carriers as it passes through the field so asto impact a printing surface 19 or a gutter 20. Gutter 20 collects thediscarded droplets and is connected to a source of vacuum, not shown,which removes the ink and usually returns it to supply 11 forrecirculation.

During operation, the formation of droplets does not always occur at thesame break-off point between charging electrodes 16 and hence, mayreceive an inappropriate charge causing erratic deflection when passingbetween electrodes 18. The variation in droplet break-off time may bedue to change in ink viscosity or temperature or for other reasons. Itis therefore important that the phase relationship between the appliedcharge and nozzle vibration causing the formation of droplets be closelycontrolled to attain accurately defined printing trajectories.

In accordance with the invention, a pulse generator designated as clockproduces pulses at a relatively high frequency, such as 1 MHz. Thesepulses are supplied to frequency divider 26, preferably at a ratio of 8to I so that the output of the frequency divider is 125 KHz. Thesesignals are supplied to the vibrator drive circuit 27 which activatestransducer 15 to thereby produce droplets at the samefrequency.

During printing, charges are applied to droplets at electrodes 16 inaccordance with signal voltages produced by character generator circuit28 through charging electrode driver 29. When droplets are to bediscarded, they are charged in accordance with a ramp voltage fromdiscard drop charging circuit which also supplies its output to driver29. Driver 29 permits the application of a discard charge only in theevent that no charging signal is received from character generator 28.In this manner, each droplet not used for printing a character is givena charge which will ultimately cause deflection into gutter 20. Theoutput wave form from driver 29 illustrates the composite of two waveforms from character generator circuit 28 and discard charging circuit30.

Printing of a character is initiated upon receipt of a characterselection signal from a source not shown. However, the generator circuitand discard charging circuit are both inoperative until receipt of aninitiation signal from a counter 31. Counter 31 is an eight positionring counter which provides an output as an initiation signal upon eachreset of the counter at a nominal rate of KHZ. The nominal counter resetfrequency is the same as the output frequency of divider circuit 26which is supplied to the nozzle vibrator. Counter 31 is advanced bypulses from clock 25 along line 32 which supplies both of two branches33 and 34. Clock pulses on line 33 pass through logical OR circuit 35and serve as one of two inputs to logical AND circuit 36. When AND 36 isfully conditioned the clock pulses are supplied through OR 37 to ringcounter 31. The clock pulses on line 34 are supplied to AND 38 which,when fully conditioned, produces pulses at AND 39. When the latter isfully conditioned, then clock pulses will appear at OR 37 forapplication to ring counter 31.

It is thus noted that counter 31 cannot be operated until the propergating signals are applied along either line 33 or line 34. Thenecessary gating signals are obtained from gutter 20 which receives thediscard ink droplets. Gutter 20 is formed with two compartments 20a and20b and is constructed in accordance with the principles disclosed inthe aforementioned patent application by .l. W. Haskell. Compartment20a, forming one impact location for discard droplets, contains thereina pair of spaced electrodes 45, indicated schematically in the drawing,which are adapted to be wet with the ink droplets falling into thatcompartment. Compartment 20b, forming a second impact location fordiscard droplets and separated by a knife edge 46, has no contacts. Bothcompartments are, of course, connected to the vacuum removal system forthe accumulated ink. Contacts 45 form the sensors to detect into whichcompartment the ink droplets are currently falling. These contacts areconnected to a voltage divider and filter network 47 to provide anelectrical output signal indicative of the presence or absence of theink droplets. This detection network comprises a pair of resistors 48and 49 connected between a positive voltage source and ground. Acapacitor 50 parallels resistor 49 and contacts 45 from ink discardcompartment 20a.

When ink droplets, which are electrically conductive, fall intocompartment 2011, they complete a circuit between the two contacts 45 tothus produce a low impedance path to ground, bypassing resistor 49, andthus establish approximately a ground potential as one input tocomparator circuit 51. However, should the discard droplets be impactingcompartment 20b, contacts 45 will be essentially open so that the inputsignal to comparator 51 will be that voltage appearing across capacitor50 and resistor 49. Comparator circuit 51 has as its second input asuitable reference voltage source and upon comparison with the detectioncircuit input will provide either a low level output, indicating dropletimpingement in compartment 20a. or a high level output, indicatingimpingement by the discard droplets in compartment 20b. The outputsignal of comparator 51 is applied to both AND 39 and inverter circuit52.

Assume for the time being that the output level from comparator 51 ishigh, and will serve as the conditioning signal for AND 39 which has asecond input from AND 38. It will be recalled that AND 38 has one inputclock pulses which are supplied along lines 32 and 34. The second inputto AND 38 is from a logical NAND circuit 53, to which one input is clockpulses on line 54, and the second which is along line 55 from a samplingpulse circuit to be described subsequently. At present, it is sufficientto assume that no pulse is present on input line 55. Therefore, witheach clock pulse, NAND 53 will not be operable since it lacks a signalon line 55 and its output will therefore be at a high level. This willfully condition AND 38 to thereby gate clock pulses from lines 32 and 34to AND 39. Hence, with the high level present from comparator 51, AND 39will be effective to transmit clock pulses to OR 37 and then to ringcounter 31. As the ring counter is cycled, each reset provides aninitiation signal at its output which starts character generator circuit28 and discard charging circuit 30 as described above.

If it is now assumed that the output level from comparator 51 is low, itwill provide a blocking signal at AND 39. However, inverter 52 willreverse the level and the high level signal will fully condition AND 36so that clock pulses appearing on lines 32 and 33 and passing OR 35 willbe gated through AND 36. The output of AND 36 is supplied to OR 37 andthence to ring counter 31.

At this point it will be seen that ring counter 31 will receive regularclock pulses through either AND 36 or AND 39, depending on whetherdiscard droplets are impacting respective locations 20a or 20b of thegutter. No change, however, occurs in the cycle time of the ringcounter, since it will be regularly receiving clock pulses at the 1 MHzfrequency through one of the alternate circuits.

A change in the phase relationship between the drop formation bytransducer and drop charging by circuits 28, 29 and 30 is controlledthrough the application of a sampling signal. This signal may beproduced at regular intervals or intermittently as desired or asnecessary to properly maintain the phase relation. In FIG. I, a samplingsignal is regularly obtained at approximate 17 ms. intervals through atransformer 60 connected across an alternating current source 61 forexample, 60 Hz. The output of the secondary winding is coupled to apulse sharpening circuit 62 whose output is connected to latch circuit63. The latch output serves as one input to AND 64 which has a secondinput applied from inverter 65 to which clock pulses are supplied online 66. Thus, AND 64 will provide a high level output during thenegative portion of the clock pulse when latch 63 is set. This output ofAND 64 sets another latch 67 and is also used to reset latch 63. Thesetting of latch 67 serves as a conditioning input for AND 68 which hasa second input clock pulses on line 66. Therefore, latch 67 will be setduring the negative portion of the clock pulse and AND 68 will produce ahigh level output on line 69 during the next positive portion of theclock pulse. The high level output on line 69 is used to reset latch 67and is supplied as a sampling signal for activating single shot 70 andconditioning NAND 53 as mentioned above.

Timing relationships between the clock pulses and initial samplingsignal to provide an output sampling signal at AND 68 are shown in thewaveforms of FIGS. 2 and 3. FIG. 2 illustrates the condition when thesampling signal initially occurs during the time the clock pulse is low(waveforms a and b). Latches 63 and 67 are both immediately set becauseof the high level output of inverter 65 (waveforms c, d, e, and f).Latch 67 being high conditions AND 68 so that a sampling signal occursat the time the clock pulse level next becomeos high (waveformsfand g).Latch 67 is reset at the fall of the clock pulse.

In FIG. 3, if the sampling signal initially arrives during the time theclock output is high, latch 63 will be set but latch 67 cannot be sinceinverter 65 blocks AND 64 (waveforms a e). Latch 67 is set when theclock output next becomes low, but AND 68 blocks any output until thenext clock high level occurs (waveforms e g).

When a sampling signal appears from AND 68 via line 69 at single shot70, the single shot is triggered by the down stroke of the samplingsignal to produce a short output pulse, the down stroke of whichtriggers a second single shot 71. The sequence of two single shots isused to insure that signals from single shot 71 occur at approximatelythe center portion of the down level of a clock pulse on line 33. (Seewaveforms d g of FIG. 4). The output from single shot 71 serves as anextra input pulse for ring counter 31. When a signal appears at theoutput of single shot 71, it passes immediately through OR 35 to AND 36.If at that time, comparator 51 is at low level, then inverter 52 and AND36 produce a signal which is supplied through OR 37 to ring counter 31as an extra pulse to advance the ring counter one position in additionto the advances normally resulting from' the clock pulses. Thus, ringcounter 31 will reach its reset point one clock period sooner andproduce an initiation signal to the character generator 28 and discardcharging circuit 30 that much earlier. AND 36 was conditioned by thecomparator circuit that indicated that discard drops were impacting atlocation 20a of gutter 20. With the earlier initiation signal suppliedto circuits 28 and 30, a charge will also be applied earlier to dropletsat charging electrodes 16. This will cause discard droplets to move toimpact location 20b because the ramp voltage is started earlier and thusis higher at the instant of drop formation.

Assume this time that comparator 51 provides a high level output(waveforms, FIG. 5). Thus, AND 36 is blocked because of inverter 52 andno pulses reach counter 31 via that route (waveform d). Further,returning now to NAND 53, when the sampling pulse is high on line and aclock pulse is at high level on line 54, NAND 53 will provide a lowlevel output to block AND 38 (waveforms f and g). Thus, during theexistence of a sampling signal on line 69 and 55, no clock pulses willpass AND 38. Although conditioned by the high level output fromcomparator 51, AND 39 will produce no output to OR 37 (waveform h).Thus, one of the clock pulses is barred from reaching ring counter 31.Upon the removal of the sampling pulse on line 69, however, clock pulseswill resume and continue to increment the ring counter. Sampling pulse69 is limited to being effective for only a single clock pulse. Sincecounter 31 has missed one of the regular clock pulses, it will producean initiation signal to the circuits 28, 29, and 30, one clock periodlater. This results in driver circuit 29 applying a delayed chargingsignal to the droplets. As a result, discard droplets that are chargedwill now impinge on impact location a.

For operation of the phase compensation device, the ink jet nozzle isoriginally aimed so that with no signal applied to the change electrodes16 in FIG. 1, the droplets will impact the gutter at compartment 20awith detection electrodes. Thereafter, the control system is energizedand every droplet that is not needed for printing goes to the gutter andgets a charge depending upon the relationship of the break-off time withthe ramp voltage produced from discard charging circuit 30. During thefirst moments of operation, the relationship is not defined, but thereis a ramp for each discard droplet. The first droplets may thus hit thepart of the gutter without the terminals, or the part with theterminals, but all droplets will impact the same part, omitting for thetime being the case where the drops are split by the divider 46. If thedroplets hit the part of the gutter' without the electrodes, resistancewill be high, as described above, so that upon the next sampling pulse,one clock pulse will be suppressed and ring counter 31 will be filledapproximately one microsecond later. The ramp for the discard dropletswill also start that much later in relation to the excitation voltageapplied to vibrator transducer 15. The discard droplets will thus see aslightly lower potential at separation time and the point of impact ongutter 20 will shift towards the divider. This process will repeatitself with each sampling pulse until the droplets cross the divider. Atthat instance, the resistance between the electrodes in compartment 20adecreases and the output signal of comparator 51 becomes low.Thereafter, a pulse will be added to the pulses coming from the clock tothe counter through AND 36, causing the ramp to start I microsecondsooner with respect to the instant of droplet break-off, thus the chargevoltage on the discard droplets will be higher, causing the impact pointto shift back toward compartment 20b without ink sensing terminals. Thisprocess of hunting will continue during the operation of the system.

If, for any reason, the instant of droplet break-off shifts with respectto the excitation voltage of the vibrator transducer 15, the system willadd or subtract pulses at the rate of one per sampling period until thenormal hunting mode is re-established.

It can readily be seen that when droplets hit the divider, suchoperation does not impair the functioning of the system. At worst, theextreme amplitude of hunting is plus or minus one-eight of the period ofexcitation of the vibrating transducer 15, an amount well withintolerable limits. It is to be noted also that although a frequency of 1MHz has been disclosed, this frequency can be changed to provide adifferent frequency at vibrator transducer 15 or ring counter 31. Thering counter may require twice the frequency and the capacity to producesmaller increments of adjustment during operation.

Although a ring counter has been disclosed as the means to produce aninitiation signal, a shift register may readily be substituted for thecounter.

From the foregoing description, it will be apparent there is provided asystem for effecting close control over the phase relations in an inkdrop printer during printing operation. The printer is corrected as tothe phase relation through the utilization of all discard drops whichcan occur during or at the end ofa character or line. Further,adjustments can be made in smaller increments than heretofore possibleand use highly accurate digital techniques.

While the invention has been particularly shown and described withreference to a preferred embodiment thereof, it will be understood bythose skilled in the art that various chages in form and details may bemade therein without departing from the spirit and scope of theinvention.

What is claimed is:

1. In an ink jet printer having a transducer for vibrating a nozzle at apredetermined frequency to produce droplets having a selected phaserelation with applied. variable, input information charges inducedthereon by an input information source energizing a charging electrodefor correspondingly varying deflection of said droplets in an electricfield between deflecting electrodes, apparatus for varying the phaserelation between said transducer vibrations and said applied chargescomprising:

circuit means connected to said charging electrode for applying, inresponse to an initiation signal, input information signals to saiddroplets and, in the absence thereof, applying calibration signals todroplets to be discarded;

means providing a train of clock pulses of fixed frequency;

frequency dividing means connected to said clock pulse means forenergizing said transducer means at said predetermined frequency;

counter means of predetermined capacity connected to said clock pulsemeans and said circuit means for cyclically counting said pulses andproducing an initiation signal during each counting cycle at saidpredetermined frequency;

detecting means for said discarded droplets having a plurality of sensorlocations, each said location producing an output signal peculiar todroplet presence thereon; and

control means responsive to said output signals to alter the number insaid train of clock pulses at said counter means during a counting cycleand change the time of said count cycle and thereby the frequency ofsaid initiation signal.

2. Apparatus as described in claim 1, wherein said control meansincludes means for generating sampling signals for enabling change ofsaid phase relation and gating means connected to said clock pulse meansand sampling signal means, being operable for selecting certain saidoutput signals to be effective to change said count cycle time.

3. Apparatus as described in claim 2, wherein said gating means isrendered operable by the occurrence of a sampling signal inpredetermined relation with one of said clock pulses.

4. Apparatus as described in claim 3 wherein said sampling signals occurat a frequency less than said calibration signal frequency.

5. Apparatus as described in claim 1, wherein said detecting means hastwo sensor locations and produces respective output pulses peculiarthereto; and

said control means is responsive to said output signals to alter saidtrain of clock pulses and initiation signals so that subsequent ones ofsaid calibration signals charge said discard droplets for deflection tothe other of said locations.

6. Apparatus as described in claim 1 wherein the output signals of eachsaid location alter thenumber of pulses in said train in a particularmanner.

7. Apparatus as described in claim 1 wherein said predeterminedcalibration signal frequency is the same as said nozzle vibrationfrequency.

8. Apparatus as described in claim 1, wherein said detecting means hasfirst and second sensor locations and produces respective first andsecond output signals; and

said control means is responsive to said first output signal to add apulse to said train of clock pulses supplied to said counter means, andis responsive to said second output signals to delete a pulse from saidtrain of clock pulses supplied to said counter means.

9. Apparatus as described in claim 1, wherein the frequency of saidclock pulses is an integral multiple of the frequency of saidcalibration signal frequency.

10. Apparatus as described in claim 1 wherein said calibration signalfrequency is the same as said nozzle vibration frequency and said clockpulse frequency is an integral multiple thereof.

1]. In an ink jet printer system wherein ink under pressure is deliveredto a nozzle which is vibrated at a predetermined frequency by atransducer means to produce a stream of drops and a charging electrodeis positioned adjacent said nozzle to charge said drops in a selectedphase relation with information signals from input information signalmeans applied to said electrode for producing deflection of said dropsin accordance with said information input signals as said drops move inan electric field between a pair of deflecting electrodes, apparatus forvarying the phase relation between the formation of said drops and saidinformation input signals comprising;

circuit means including calibration signal means and said inputinformation signal means connected to said charging electrode forapplying to said charging electrode, in response to an initiationsignal, calibration signals and information input signals so that alldrops not charged by said information input signals are charged by saidcalibration signals;

a source of clock pulses of fixed frequency;

frequency dividing means connected to said clock pulse source forenergizing said transducer means at said predetermined frequency;

pulse counter means connected to said source and said circuit means forsupplying an initiating signal at said predetermined frequency to saidinput information signal means and said calibration signal meansconcurrently;

means for detecting said drops receiving a calibration charge thereonand for producing first and second output signals indicativerespectively of the drop presence in a first location and in a secondlocation thereon;

means responsive to said first output signals from said detecting meansfor adding a count to said counter means; and

means responsive to said second output signals from said detecting meansfor deleting a count from said pulse train to said counter means.

12. In an ink jet printer system in which pressurized ink issues from anozzle vibrated by a transducer means to produce a stream of dropletsthat receive in a selected phase relation from a charging electrode atthe time of formation a charge representative of information from aninformation input means to establish a subsequent marking or discardposition upon passing through an electric field between a pair ofdeflection electrodes, apparatus for varying the phase relation betweensaid transducer vibration and said applied charge comprising:

circuit means including calibration signal means and said informationinput signal means connected to said charging electrode for applying, inresponse to an initiation signal, said calibration signal and saidinformation input signals to said charging electrode so that all dropsnot charged by information input signals are charged by said calibrationsignal for discard;

gutter means catching said discard drops operable to produce first andsecond output signals indicative of drop impact in a first or a secondlocation thereon, respectively;

clock pulse means for producing a train of pulses at a fixed frequencygreater than that of said calibration signal;

frequency dividing means connected to said clock pulse means forenergizing said transducer means at said predetermined frequency;

counter means of predetermined capacity connected to said circuit meansand advanced by said clock means operable to provide an initiatingsignal at said predetermined frequency to said charging circuit meansupon each reset of counter means; and means responsive to said firstsignals from said gutter means for deleting one of said train of pulsesfrom said clock means and operable in response to said second signalsfor inserting a pulse in said train of pulses to said counter means.

1. In an ink jet printer having a transducer for vibrating a nozzle at apredetermined frequency to produce droplets having a selected phaserelation with applied, variable, input information charges inducedthereon by an input information source energizing a charging electrodefor correspondingly varying deflection of said droplets in an electricfield between deflecting electrodes, apparatus for varying the phaserelation between said transducer vibrations and said applied chargescomprising: circuit means connected to said charging electrode forapplying, in response to an initiation signal, input information signalsto said droplets and, in the absence thereof, applying calibrationsignals to droplets to be discarded; means providing a train of clockpulses of fixed frequency; frequency dividing means connected to saidclock pulse means for energizing said transducer means at saidpredetermined frequency; counter means of predetermined capacityconnected to said clock pulse means and said circuit means forcyclically counting said pulses and producing an initiation signalduring each counting cycle at said predetermined frequency; detectingmeans for said discarded droplets having a plurality of sensorlocations, each said location producing an output signal peculiar todroplet presence thereon; and control means responsive to said outputsignals to alter the number in said train of clock pulses at saidcounter means during a counting cycle and change the time of said countcycle and thereby the frequency of said initiation signal.
 2. Apparatusas described in claim 1, wherein said control means includes means forgenerating sampling signals for enabling change of said phase relationand gating means connected to Said clock pulse means and sampling signalmeans, being operable for selecting certain said output signals to beeffective to change said count cycle time.
 3. Apparatus as described inclaim 2, wherein said gating means is rendered operable by theoccurrence of a sampling signal in predetermined relation with one ofsaid clock pulses.
 4. Apparatus as described in claim 3 wherein saidsampling signals occur at a frequency less than said calibration signalfrequency.
 5. Apparatus as described in claim 1, wherein said detectingmeans has two sensor locations and produces respective output pulsespeculiar thereto; and said control means is responsive to said outputsignals to alter said train of clock pulses and initiation signals sothat subsequent ones of said calibration signals charge said discarddroplets for deflection to the other of said locations.
 6. Apparatus asdescribed in claim 1 wherein the output signals of each said locationalter the number of pulses in said train in a particular manner. 7.Apparatus as described in claim 1 wherein said predetermined calibrationsignal frequency is the same as said nozzle vibration frequency. 8.Apparatus as described in claim 1, wherein said detecting means hasfirst and second sensor locations and produces respective first andsecond output signals; and said control means is responsive to saidfirst output signal to add a pulse to said train of clock pulsessupplied to said counter means, and is responsive to said second outputsignals to delete a pulse from said train of clock pulses supplied tosaid counter means.
 9. Apparatus as described in claim 1, wherein thefrequency of said clock pulses is an integral multiple of the frequencyof said calibration signal frequency.
 10. Apparatus as described inclaim 1 wherein said calibration signal frequency is the same as saidnozzle vibration frequency and said clock pulse frequency is an integralmultiple thereof.
 11. In an ink jet printer system wherein ink underpressure is delivered to a nozzle which is vibrated at a predeterminedfrequency by a transducer means to produce a stream of drops and acharging electrode is positioned adjacent said nozzle to charge saiddrops in a selected phase relation with information signals from inputinformation signal means applied to said electrode for producingdeflection of said drops in accordance with said information inputsignals as said drops move in an electric field between a pair ofdeflecting electrodes, apparatus for varying the phase relation betweenthe formation of said drops and said information input signalscomprising; circuit means including calibration signal means and saidinput information signal means connected to said charging electrode forapplying to said charging electrode, in response to an initiationsignal, calibration signals and information input signals so that alldrops not charged by said information input signals are charged by saidcalibration signals; a source of clock pulses of fixed frequency;frequency dividing means connected to said clock pulse source forenergizing said transducer means at said predetermined frequency; pulsecounter means connected to said source and said circuit means forsupplying an initiating signal at said predetermined frequency to saidinput information signal means and said calibration signal meansconcurrently; means for detecting said drops receiving a calibrationcharge thereon and for producing first and second output signalsindicative respectively of the drop presence in a first location and ina second location thereon; means responsive to said first output signalsfrom said detecting means for adding a count to said counter means; andmeans responsive to said second output signals from said detecting meansfor deleting a count from said pulse train to said counter means.
 12. Inan ink jet printer system in which pressurized ink issues from a nozzlevibrated by a traNsducer means to produce a stream of droplets thatreceive in a selected phase relation from a charging electrode at thetime of formation a charge representative of information from aninformation input means to establish a subsequent marking or discardposition upon passing through an electric field between a pair ofdeflection electrodes, apparatus for varying the phase relation betweensaid transducer vibration and said applied charge comprising: circuitmeans including calibration signal means and said information inputsignal means connected to said charging electrode for applying, inresponse to an initiation signal, said calibration signal and saidinformation input signals to said charging electrode so that all dropsnot charged by information input signals are charged by said calibrationsignal for discard; gutter means catching said discard drops operable toproduce first and second output signals indicative of drop impact in afirst or a second location thereon, respectively; clock pulse means forproducing a train of pulses at a fixed frequency greater than that ofsaid calibration signal; frequency dividing means connected to saidclock pulse means for energizing said transducer means at saidpredetermined frequency; counter means of predetermined capacityconnected to said circuit means and advanced by said clock meansoperable to provide an initiating signal at said predetermined frequencyto said charging circuit means upon each reset of counter means; andmeans responsive to said first signals from said gutter means fordeleting one of said train of pulses from said clock means and operablein response to said second signals for inserting a pulse in said trainof pulses to said counter means.